The present invention relates to an image heating device permitting reduction of warm-up time and an image forming apparatus. More particularly, the present invention relates to an image heating device for use in image forming apparatus, such as electrophotographical apparatus or electrostatic recording apparatus, that is suitable as a fixing device for fixing unfixed images, and to an image forming apparatus.
Conventionally, as image heating devices, for which fixing devices are a typical example, contact-heating devices such as heat roller type devices and belt type devices, generally have been used.
In recent years, due to the demand for shorter warm-up time and reduced energy consumption, electromagnetic induction heating, by which rapid heating and high efficiency heating are likely to be attained, are attracting great attention (see JP 10(1998)-123861 A).
FIG. 23 shows a cross-sectional view of an image heating device utilizing the electromagnetic induction, which is disclosed in JP 10(1998)-123861 A. As shown in FIG. 23, a magnetization coil 114 is provided inside a heat-generating roller 112. By this magnetization coil 114 and a core 117, an alternating magnetic field is generated to induce an eddy current in the heat-generating roller 112, thereby heating the heat-generating roller 112. Then, an unfixed toner image 111 formed on recording paper 110 can be fixed after the recording paper 110 has passed through a nip portion formed between the heat-generating roller 112 and a pressure roller 113. Further, an image heating device with a heat-generating roller that is made thin has been proposed, as disclosed in JP 10(1998)-74007 A. FIG. 24 shows this device.
In FIG. 24, reference numeral 310 denotes a magnetization coil, which generates a high-frequency field when a high-frequency current is applied thereto from an inverter circuit, and reference numeral 311 denotes a metal sleeve, which generates heat through electromagnetic induction and is rotated. An external pressure member 313 rotates in arrow direction xe2x80x9caxe2x80x9d. The metal sleeve 311, which is held between the external pressure member 313 and an internal pressure member 312, rotates following the external pressure member 313.
A recording paper 314 carrying an unfixed toner image thereon is fed to the nip portion formed between the external pressure member 313 and the internal pressure member 312 in the arrow direction shown in the drawing. The unfixed toner image on the recording paper 314 is then fixed by the heat from the metal sleeve 311 and the pressure from both the pressure members 312 and 313.
Further, to prevent electromagnetic induction heating from being performed while the metal sleeve 311 is at rest, a heating signal for the inverter circuit is set to be a logical product of an operation signal and a heating signal from a drive motor for rotating the external pressure member 313.
In image heating devices utilizing such electromagnetic induction, a heat-generating member such as a heat-generating roller or the like is directly heated through electromagnetic induction. Such image heating devices thus can attain higher heat-exchanging efficiency as compared with those using a halogen lamp for heating, so that the surface of a fixing roller can be heated up to a fixing temperature rapidly with a smaller power.
However, the image heating device in which a normal metal heat-generating roller is simply heated through electromagnetic induction cannot attain remarkably reduced warm-up time as compared with conventional image heating devices using a halogen lamp for heating.
Further, if a heat generating roller is made thinner to decrease the thermal capacity for shortening warm-up time, it becomes difficult to control the temperature of the roller.
JP 8(1996)-137306 A has proposed an image heating device using a belt with a smaller thermal capacity for shortening warm-up time. In this image heating device, the belt formed of a conductive material is heated through electromagnetic induction and the belt itself thus can be heated rapidly. However, since the thermal capacity of the belt is too small, the heat generated by the belt is removed by a tension roller and an oil roller, which brings about a problem that it is difficult to raise the temperature of the entire system.
For shortening warm-up time, a rotating operation of the heat-generating roller is generally started after the heat-generating roller is heated up to a predetermined temperature. However, since the roller can be heated rapidly according to the electromagnetic induction heating, if the heat-generating roller at rest is heated in the image heating device with a small thermal capacity, an abrupt temperature rise may occur at a portion of the heat-generating roller. This may result in deterioration of the belt, an elastic material provided on the belt, and the like.
Especially in an image heating device performing heating with a heat-generating roller and a heat-resistant belt looped around the roller, the temperature of the heat-generating roller is made too high by the rapid heating, resulting in permanent set of the heat-resistant belt in accordance with the curvature of the roller. It is to be noted here that this problem seldom occurs in the case of a conductive belt and never occurs in an image heating device in which a straight portion of the belt is heated. This problem occurs only in an image heating device in which a heat generating roller is heated and the heat from the roller is conveyed by the belt formed of a resin.
From the viewpoint of saving energy, it is preferable that a heat-generating member in an image heating device is heated only when the device is used. Image heating devices of heat roller type generally include a heat-generating member in a nip portion. However, in image heating devices of the belt type, a heat-generating member is away from a nip portion, resulting in time lag between the temperature change in the heat-generating member and in the nip portion.
In addition, in the image heating devices in which the heat-generating member is away from the nip portion, the heat from the belt, which has been heated by the heat-generating member, is not only consumed for melting toner on recording paper but also for heating a pressure roller and a fixing roller. The pressure roller and the fixing roller are heated by removing the heat from the belt. Accordingly, the amount of the heat removed by these rollers depends on the amount of the belt that has been passed, i.e., the process speed. The heat removed by these rollers is not directly involved in the fixing operation. Therefore, it is necessary to minimize the amount of this wasted heat for performing the fixing operation quickly.
In an image heating device including a magnetization coil and a rotatable conductive heating element, if the device is configured so that the conductive heating element is heated through electromagnetic induction only when the element is rotating, the magnetization coil should magnetize the element after a rotating operation of the element is started. Otherwise, the temperature of the element is only partially made high, resulting in uneven temperature distribution. Although this configuration permits a relatively short warm-up time, it is necessary that the conductive heating element keeps residual heat during a standby period for immediately satisfying the user""s demands for printing. However, in the image heating device with this configuration, a rotating operation of the conductive heating element has to be performed for heating the element, which brings about a problem that the element needs to be kept rotating even in the standby period. Besides, since the conductive heating element is heated rapidly, it is difficult to maintain the element at low temperatures.
In the belt-type image heating device, if a temperature sensor is provided on the surface of the belt, the sensor is liable to damage the surface of the belt, thereby reducing the life of the belt. On this account, there has been an attempt to provide the temperature sensor at a portion that is not in contact with the belt on the surface of the heat-generating roller. In this case, however, the temperature sensor cannot accurately determine the amount of the heat removed from the belt and an appropriate amount of heating thus cannot be performed. On the other hand, when the temperature sensor is merely attached to the inner peripheral surface of the belt, accurate determination of the temperature is made difficult by variations in measured temperatures due to vibration or snaking of the belt.
If the heat-generating member is heated through electromagnetic induction while it is at rest, only a portion of the heat-generating member is extremely heated up, which may exceed the heat resistant temperature of the heat-generating member or any other members in contact with the heat-generating member. This may result in thermal alteration and thermal deformation of the member(s), which cause to degrade the quality of resultant images.
In the above-mentioned image heating device, only the operation signal to the drive motor is taken into consideration. Accordingly, the device is not capable of dealing with the trouble occurring in the path for transporting the driving force from the drive motor to the image heating device. Particularly, in the image heating device configured to be freely attachable/detachable to/from the image forming apparatus main body, insufficient installation, damage to the gear for transporting the driving force from the drive motor, and the like are liable to occur, which may lead to a problem that the heat-generating member does not rotate while the drive motor is rotating.
The present invention has been made to overcome the above-mentioned problems of the prior art. It is an object of the present invention to provide an image heating device with a small capacity that can be heated rapidly and an image forming apparatus. It is a further object of the present invention to provide an image forming apparatus including an image heating device requiring a short warm-up time, which can deal with abnormal conditions and thus can be used stably.
In order to achieve the above objects, an image heating device according to a first configuration of the present invention includes a belt having a heat resistance; a rotatable heat-generating member, which is at least partially conductive and arranged in contact with an inner peripheral surface of the belt; a fixing roller, the fixing roller and the heat-generating member movably suspending the belt therebetween; and a magnetization means for heating the heat-generating member through magnetization, which is arranged outside the heat-generating member. The image heating device according to the first configuration is characterized in that the magnetization means heats the heat-generating member through magnetization after a rotating operation of the heat-generating member is started.
If the magnetization means heats the heat-generating member through magnetization before the rotating operation of the heat-generating member is started, a temperature of the heat-generating member is only partially made abnormally high, thereby causing alternation of the heat-resistant belt that is in contact with the heat-generating member, as well as permanent set of the belt in accordance with the curvature of the heat-generating member. Further, if the surface of the belt is coated with an elastic layer made of silicone rubber, for example, a temperature of the belt is only partially made high, thereby causing alternation or peeling of this elastic layer. However, in the image heating device according to the first configuration of the present invention, the problems as above never arise because the magnetization means heats the heat-generating member through magnetization after the rotating operation of the heat-generating member is started. On the other hand, in the image heating device configured so that the entire heat-generating member is heated at one time by the magnetization means provided inside the heat-generating member, it is possible to heat the heat-generating member while it is at rest. In this case, however, since a temperature of the magnetization means is made high, there is a concern about a heat resistance of the magnetization means. In contrast, in the image heating device according to the first configuration of the present invention, since the magnetization means is provided outside the heat-generating member, it is possible to cool the magnetization means.
An image heating device according to a second configuration of the present invention includes a rotatable belt having a heat resistance; a heat-generating member, which is at least partially conductive and arranged in contact with an inner peripheral surface of the belt; a fixing roller, the fixing roller and the heat-generating member movably suspending the belt therebetween; and a magnetization means for heating the heat-generating member through magnetization, which is arranged outside the heat-generating member. The image heating device according to the second configuration is characterized in that the magnetization means heats the heat-generating member through magnetization only when a rotating operation of the belt is being performed. The image heating device according to this second configuration exhibits the same effect as that in the image heating device according to the above-mentioned first configuration.
The above-mentioned first and second configurations of an image heating device according to the present invention is effective in the case where a portion of the heat-generating member to be heated by the magnetization means has a certain curvature, and the belt is heated by heat from the portion with the certain curvature.
Further, in the above-mentioned first and second configurations of an image heating device according to the present invention, it is preferable that a glass transition point of the belt is 200xc2x0 C. to 500xc2x0 C. When the glass transition point of the belt is less than 200xc2x0 C., it is difficult to use the belt as a fixing belt. On the other hand, when the glass transition point of the belt is more than 500xc2x0 C., care about heating as described above need not be taken.
Further, in the above-mentioned first and second configurations of an image heating device according to the present invention, it is preferable that not more than ⅔ of a total outer area of the heat-generating member is heated by the magnetization means. In the case where more than ⅔ of the total outer area of the heat-generating member is heated by the magnetization means, heat remaining in the magnetization means does not escape easily, which leads to the same problem about heat as that in the image heating device in which the magnetization means is provided inside the heat-generating member.
Furthermore, in the above-mentioned first and second configurations of an image heating device according to the present invention, it is preferable that a thermal capacity of the heat-generating member is not more than 60 J/K. According to this preferable example, the heat-generating member can be heated up to 200xc2x0 C. or more in about one second when the heat-generating member is heated with 1000 W of electric power being applied to the heat-generating member. In practice, since heating is not performed on the entire heat-generating member, a thermal capacity of only the portion that is really heated is considered to be not more than half the above-mentioned value. Accordingly, it is considered that the heat-generating member can be heated up to 400xc2x0 C. or more in about one second. This becomes increasingly significant as the heat-generating member is made thinner. Accordingly, if heating by the magnetization means is started first, a rotating operation needs to be started in one second. In addition, in the case where the thermal capacity of the heat generating member is not more than 30 J/K, the heat-generating member can be heated up to hundreds of degrees in one second when the heat-generating member is heated with 500 W of electric power being applied to the heat-generating member. Moreover, when the thermal capacity of the heat-generating member is not more than 20 J/K, the heat-generating member may be heated up to hundreds of degrees in a moment. Therefore, it is essential that the heat-generating member or the belt is rotated.
Still further, in the above-mentioned first and second configurations of an image heating device according to the present invention, it is preferable that the magnetization means is a magnetization coil.
In the above-mentioned first configuration of an image heating device according to the present invention, it is preferable that the rotating operation of the heat-generating roller is terminated after the magnetization of the heat-generating roller by the magnetization means is terminated.
Further, in the above-mentioned first and second configurations of an image heating device according to the present invention, it is preferable that the belt is rotated at least until a furthest upstream point in a rotating direction of a portion in which the belt and the heat-generating member both at rest are in contact with each other at a certain curvature separates from the heat-generating member before heating of the heat-generating member is started. If the belt remains at rest for a long time while maintaining a certain curvature, the belt may be deformed temporarily in accordance with the curvature. Such deformation can be restored if the belt is rotated while being heated. However, if the belt is heated while it is at rest, the belt is liable to be permanently set. Therefore, heating of the heat-generating member needs to be started after the portion of the belt that is in contact with the heat-generating member when the belt is at rest and is deformed in accordance with a certain curvature separates from the heat-generating member.
An image heating device according to a third configuration of the present invention includes a belt having a heat resistance; a first support roller arranged in contact with an inner peripheral surface of the belt; a second support roller, the second support roller and the first support roller movably suspending the belt therebetween; and a magnetization means for heating at least one of the first support roller and the belt through magnetization. The image heating device according to the third configuration is characterized in that the belt is rotated at least until a furthest upstream point in a rotating direction of a portion in which the belt and the first support roller both at rest are in contact with each other at a certain curvature separates from the first support roller before heating of the heat-generating member is started.
An image heating device according to a fourth configuration of the present invention includes a belt having a heat resistance; a rotatable heat-generating member, which is at least partially conductive and arranged in contact with an inner peripheral surface of the belt; a fixing roller, the fixing roller and the heat-generating member movably suspending the belt therebetween; a pressure roller arranged in opposition to the fixing roller, the pressure roller and the belt forming a nip portion therebetween; and a magnetization means for heating the heat-generating member through magnetization, which is arranged outside the heat-generating member. The image heating device according to the fourth configuration is characterized in that heating of the heat-generating member by the magnetization means is terminated while a recording material is passing through the nip portion.
In the case of an image heating device of belt type, a heat-generating member is away from a nip portion. Accordingly, if the heating of the heat-generating member by the magnetization means is terminated after the recording material has passed through the nip portion, time lag is generated between the temperature change in the heat-generating member and in the nip portion. In order to terminate heating immediately after fixing is completed from the viewpoint of saving energy, it is necessary to terminate the heating of the heat-generating member by the magnetization means when a distance between the nip portion and a terminal end of the recording material becomes shorter than a distance between a point where the belt separates from the heat-generating member and the nip portion. By doing so, heating can be terminated when the belt has stored a sufficient amount of heat for melting toner on the recording material.
An image heating device according to a fifth configuration of the present invention includes a magnetization means; and a rotatable conductive heat-generating body to be heated by the magnetization means, with the magnetization means heating the conductive heat-generating body through magnetization after a rotating operation of the conductive heat-generating body is started. The image heating device according to the fifth configuration is characterized in that the conductive heat-generating body is rotated at a first speed when a temperature thereof is less than a predetermined set temperature and at a second speed when a temperature thereof is not less than the predetermined set temperature. This is because the time required for raising temperatures varies depending on rotational speeds. To shorten the time required for raising temperatures, it is important to prevent the heat of heat-generating body from being removed by other members as well as to increase the speed at which the conductive heat-generating body is heated. A typical example of members removing the heat from the conductive heat-generating body is a pressure roller. When the pressure roller is at rest, the pressure roller removes only a small amount of heat from the conductive heat-generating body because it removes heat only from the portion contacting the fixing roller. However, when the pressure roller is rotating, the entire pressure roller removes heat from the conductive heat-generating body. Accordingly, the amount of heat removed by the pressure roller increases in accordance with increase in the rotational speed of the pressure roller. On this account, by rotating the conductive heat-generating body at a low speed when raising the temperature of the conductive heat-generating body and then changing the speed to a normal speed (i.e., the speed at the time of routine operations) when the temperature of the conductive heat-generating body has reached a predetermined temperature, the time required for raising the temperature can be shortened.
In the case of an image heating device of belt type including a fixing roller and a pressure roller, a more significant effect can be obtained because the fixing roller also removes heat from the conductive heat-generating body.
In OHP mode, fixing is performed at a speed of not more than half the normal speed. In addition, in the OHP mode, since a transmittance varies considerably as affected by a temperature of the pressure roller, it is necessary that the pressure roller also be heated. In OHP mode, if the conductive heat-generating body is operated at a speed of half the normal speed from the beginning, the temperature rise in the pressure roller is made slow. However, by rotating the conductive heat-generating body at the normal speed when heating the conductive heat-generating body and then reducing the speed to half the normal speed when the temperature of the conductive heat-generating body has reached a predetermined temperature, the heat-generating body can be rapidly heated up to a fixing temperature at which a sufficient OHP transmittance is obtained.
Further, in the above-mentioned fifth configuration of an image heating device according to the present invention, it is preferable that the magnetization means is a magnetization coil for heating the conductive heat-generating body through magnetization, which is arranged outside the conductive heat-generating body.
Furthermore, in the above-mentioned fifth configuration of an image heating device according to the present invention, it is preferable that the image heating device further includes a belt formed of a heat-resistant resin, whose inner peripheral surface is in contact with the conductive heat-generating body; and a fixing roller, the fixing roller and the conductive heat-generating body movably suspending the belt therebetween.
Still further, in the above-mentioned fifth configuration of an image heating device according to the present invention, it is preferable that the first speed is not more than ⅔ of the second speed.
An image heating device according to a sixth configuration of the present invention includes a magnetization means; and a rotatable conductive heat-generating body to be heated by the magnetization means, the magnetization means heating the conductive heat-generating body through magnetization after a rotating operation of the conductive heat-generating body is started, the rotating operation of the conductive heat-generating body being terminated after the heating of the conductive heat-generating body by the magnetization means is terminated. The image heating device according to the sixth configuration is characterized in that the conductive heat-generating body is rotated at a speed slower than that at a time of routine operations during a standby period.
In an image heating device according to the present invention, to further shorten the elapsed time until printing is completed, it is necessary that the image heating device keeps residual heat even in a standby period. However, in the image heating device according to the present invention, it is difficult to raise the temperature of an fixing unit while maintaining the unit at rest, as performed in the conventional image heating device using a halogen lamp for heating. A rotating operation is thus required even when the image heating device maintains residual heat. However, if the same operation as that during routine operations is performed during a standby period, it is too noisy and the life of the image heating device is shortened. On this account, during a standby period, it is necessary to rotate the conductive heat-generating body at a speed slower than that at a time of routine operations.
Further, in the above-mentioned sixth configuration of an image heating device according to the present invention, it is preferable that the magnetization means is a magnetization coil for heating the conductive heat-generating body through magnetization, which is arranged outside the conductive heat-generating body.
Furthermore, in the above-mentioned sixth configuration of an image heating device according to the present invention, it is preferable that the image heating device further includes a belt formed of a heat-resistant resin, whose inner peripheral surface is in contact with the conductive heat-generating body; and a fixing roller, the fixing roller and the conductive heat-generating body movably suspending the belt therebetween.
Still further, in the above-mentioned sixth configuration of an image heating device according to the present invention, it is preferable that the conductive heat-generating body is rotated at a speed not more than xc2xd of a speed at a time of routine operations during a standby period. When the maximum electric power is applied to the conductive heat-generating body, the temperature of the conductive heat-generating body is raised abruptly. Accordingly, when the conductive heat-generating body maintains residual heat, the reduced electric power should be applied to the heat-generating body.
Still further, in the above-mentioned sixth configuration of an image heating device according to the present invention, it is preferable that the conductive heat-generating body is rotated intermittently during a standby period.
Still further, in the above-mentioned sixth configuration of an image heating device according to the present invention, it is preferable that the conductive heat-generating body starts to rotate when a temperature thereof becomes less than a first set temperature and stops rotating immediately or after an elapse of a certain time period when a temperature thereof becomes not less than a second set temperature.
As described above, while the heat-generating body keeps residual heat, it is not necessary to operate the conductive heat-generating member continuously. It is sufficient that the conductive heat-generating member starts to rotate when a temperature thereof becomes less than a predetermined first temperature and stops rotating when a temperature thereof becomes not less than a predetermined second temperature. The rotating operation may be stopped immediately after the heating is stopped. However, it is preferable that the rotating operation is stopped after an elapse of a certain time period after the heating is stopped. This can be a measure for the case where there is a small amount: of overshoot after the heating is stopped.
Still further, in the above-mentioned sixth configuration of an image heating device according to the present invention, it is preferable that, during a standby period, an output lower than that during a warm-up period is applied to the magnetization means.
An image heating device according to a seventh configuration of the present invention includes a belt having a heat resistance; a rotatable heat-generating member arranged in contact with an inner peripheral surface of the belt; a fixing roller, the fixing roller and the heat-generating member movably suspending the belt therebetween; and a pressing member arranged in contact with an outer peripheral surface of the belt. The image heating device according to the seventh configuration is characterized in that a temperature sensor is provided so as to be in contact with an inner peripheral surface of the belt and in opposition to the pressing member between the heat-generating member and the fixing roller.
In an image heating device of belt type, temperature measurement preferably is performed in a portion between the nip portion and the heat-generating member to reflect the amount of heat removed by fixing. However, if the temperature sensor is pressed against the surface of the belt, which is made thin, the surface of the belt is damaged to reduce the life thereof, thereby causing defective images to be obtained. On this account, it is preferable that the temperature sensor is pressed against the rear surface of the belt. In this case, however, the temperature sensor cannot perform accurate temperature measurement without a pressing member opposing the temperature sensor via the belt, due to vibration or snaking of the belt. Therefore, by providing the temperature sensor on the side of the rear surface of the belt so as to oppose a member pressing the belt on the side of the surface of the belt, e.g., an oil application roller or a cleaning roller, the temperature sensor can perform accurate temperature measurement without damaging the belt. In the image heating devices employing electromagnetic induction heating, rapid heating and subtle temperature control can be performed. In such devices, this configuration is more effective since temperature measurement of the belt thus becomes important.
Further, in the above-mentioned seventh configuration of an image heating device according to the present invention, it is preferable that the image heating device further includes a magnetization means arranged outside the heat-generating member; the heat-generating member being at least partially conductive, the heat-generating member being heated by the magnetization means through electromagnetic induction.
An image forming apparatus according to a first configuration of the present invention includes an image forming means for forming an unfixed image onto a recording material and having the unfixed image carried thereon; and a fixing device for fixing the unfixed image onto the recording material. The image forming apparatus according to the first configuration is characterized in that an image heating device as described above is used as the fixing device.
An image forming apparatus according to a second configuration of the present invention includes a heat-generating member; a magnetization coil for heating the heat-generating member through electromagnetic induction, which is arranged in opposition to the heat-generating member; an inverter circuit for supplying a high-frequency current to the magnetization coil; a control unit for controlling an operation of the inverter circuit; and a temperature sensor for transmitting a signal for temperature control to the control unit, which is arranged in the heat-generating member at a portion other than a portion that is heated most by the magnetization coil.
When the temperature sensor is provided in the heat-generating member on the surface opposing the magnetization means, which is the portion heated most in the heat-generating member, the heat-generating member and the magnetization coil are spaced away, resulting in a degraded electromagnetic coupling between the heat-generating member and the magnetization coil. On the other hand, when the magnetization coil is formed in a shape avoiding the temperature sensor, the amount of the heat generated from the heat-generating member decreases only at the portion where the temperature sensor is provided, resulting in uneven temperature distribution.
Further, in the above-mentioned second configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a driving source for rotationally driving the heat-generating member; and a rotation detecting means for detecting rotation of the heat-generating member, the heat-generating member being rotatable, the magnetization coil being arranged in opposition to a peripheral surface of the heat-generating member.
Furthermore, in the above-mentioned second configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a rotatable member, which rotates while keeping in contact with the heat-generating member; a driving source for rotationally driving the rotatable member; and a rotation detecting means for detecting rotation of the rotatable member, the heat-generating member being at least partially formed of a conductive material.
Still further, in the above-mentioned second configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a rotatable member, which rotates while keeping in contact with the heat-generating member; a driving source for rotationally driving one of the heat-generating member and the rotatable member without using the other; a rotation detecting means for detecting rotation of the heat-generating member or the rotatable member, the heat-generating member being rotatable, the magnetization coil being arranged in opposition to a peripheral surface of the heat-generating member.
Still further, in the above-mentioned second configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a rotatable member, which rotates while keeping in contact with the heat-generating member; a driving source for rotationally driving one of the heat-generating member and the rotatable member without using the other; a driven member, which is driven via the heat-generating member or the rotatable member, and a rotation detecting means for detecting rotation of the driven member, the heat-generating member being rotatable, the magnetization coil being arranged in opposition to a peripheral surface of the heat-generating member.
Further, it is preferable that an operation of the inverter circuit is started by the control unit after a detecting signal is produced by the rotation detecting member.
Furthermore, it is preferable that an operation of the inverter circuit is stopped by the control unit when a signal from the rotation detecting member is not obtained for a predetermined time period.
Still further, it is preferable that rotation of the heat-generating member and the rotatable member is performed along with an operation of the inverter circuit.
Further, in the above-mentioned second configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a fixing unit comprising the heat-generating member and the fixing unit is freely attachable/detachable to/from an image forming apparatus main body.
An image forming apparatus according to a third configuration of the present invention includes a fixing belt; first and second support rollers for rotatably supporting the fixing belt; a magnetization coil for heating at least one of the first support roller and the fixing belt through electromagnetic induction, which is arranged in opposition to the fixing belt looped around the first support roller; an inverter circuit for supplying a high-frequency current to the magnetization coil; a control unit for controlling an operation of the inverter circuit; and a temperature sensor for transmitting a signal for temperature control to the control unit, which is arranged in at least one of the first support roller and the fixing belt at a portion other than a portion that is heated most by the magnetization coil.
Further, in the above-mentioned third configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a pressure member, which rotates while being pressed against the second support roller via the fixing belt; a driving means for rotationally driving the pressure member; and a rotation detecting means for detecting rotation of the pressure member.
Furthermore, in the above-mentioned third configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a driving means for rotationally driving at least one of the first support roller and the second support roller without using the fixing belt; and a rotation detecting means for detecting rotation of the support roller that is driven by the driving means.
Still further, in the above-mentioned third configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a pressure member, which rotates while being pressed against the second support roller via the fixing belt; a driving means for rotationally driving one of the first support roller and the second support roller without using the fixing belt; and a rotation detecting means for detecting rotation of the support roller that is rotationally driven via rotation of the fixing belt.
Still further, in the above-mentioned third configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a pressure member, which rotates while being pressed against the second support roller via the fixing belt; a driving means for rotationally driving one of the first support roller and the second support roller without using the fixing belt; and a rotation detecting means for detecting rotation of the pressure member.
Further, it is preferable that the support roller that is rotated without using the fixing belt does not generate heat.
Furthermore, in the above-mentioned third configuration of an image forming apparatus according to the present invention, it is preferable that the image heating device further includes a pressure member, which rotates while being pressed against the second support roller via the fixing belt; a driving means for rotationally driving the pressure member; and a rotation detecting means for detecting rotation of a member that rotates following the pressure member.
Further, it is preferable that an operation of the inverter circuit is started by the control unit after a detecting signal is produced by the rotation detecting means.
Furthermore, it is preferable that an operation of the inverter circuit is stopped by the control unit when a signal from the rotation detecting means is not obtained for a predetermined time period.
Further, in the above-mentioned third configuration of an image forming apparatus according to the present invention, it is preferable that the image forming apparatus further includes a fixing unit comprising the fixing belt, the first and second support rollers and the fixing unit is freely attachable/detachable to/from an image forming apparatus main body.
An image forming apparatus according to a fourth configuration of the present invention includes a heat-generating member, which is at least partially formed of a conductive material; a rotatable detecting member; a magnetization coil for heating the heat-generating member through electromagnetic induction, which is arranged in opposition to a peripheral surface of the heat-generating member; an inverter circuit for supplying a high-frequency current to the magnetization coil; a control unit for controlling an operation of the inverter circuit; a temperature sensor for transmitting a signal for temperature control to the control unit, which is arranged in the heat-generating member at a portion other than a portion that is heated most by the magnetization coil; a rotating means for rotationally driving the rotatable detecting member directly or indirectly; and a rotation detecting means for detecting rotation of the rotatable detecting member. The image forming apparatus according to the fourth configuration is characterized in that a fixing unit comprising at least the heat-generating member and the rotatable detecting member is freely attachable/detachable to/from an image forming apparatus main body.
Further, in the above-mentioned fourth configuration of an image forming apparatus according to the present invention, it is preferable that the rotation detecting means is provided in the fixing unit.
Further, in the above-mentioned fourth configuration of an image forming apparatus according to the present invention, it is preferable that the rotation detecting means is provided in the image forming apparatus main body.